1. Field of the Invention
The present invention relates to wireless sensor networks. More specifically, the present invention relates to a method and an apparatus for optimizing convergecast operations in a wireless sensor network.
2. Related Art
A convergecast operation is a type of many-to-one communication operation in a wireless sensor network in which some or all nodes in the network send data to a base-station during a relatively short time period. Convergecast operations are desirable in applications requiring periodic global state snapshots, such as in node residual energy monitoring operations, or in event-driven computations, such as a sniper localization application. In these applications, all of the data packets generated in the network have to be transmitted to a base-station for record-keeping or for intensive computational-analysis.
Generally, a time bound on convergecast latency and a guarantee on packet delivery are desirable in mission critical applications, e.g., surveillance and security applications. Specifically, a minimum convergecast latency facilitates timely detection of events which occur. Furthermore, a known time bound on the convergecast latency can help the base-station to schedule convergecast requests and related computations more effectively. Additionally, a high data delivery rate is desirable during a convergecast operation to allow the system to generate a more accurate picture of the sensing field.
Unfortunately, existing convergecast scheduling techniques are primarily based on contention-based medium access control (MAC) protocols, such as carrier sense multiple access (CSMA). When these techniques are employed during a convergecast operation, data packet collisions at sensors nodes create a major challenge, and can cause serious data losses. Furthermore, using recovery methods such as retransmission to remedy these data losses inevitably increases convergecast latency and leads to more collisions in high data rate applications, in addition to consuming extra energy. A radially coordinated transmission delay has been proposed to decrease the probability of collisions. However, as a result of using CSMA at the MAC layer, the additional convergecast latency resulting from radial coordination is far from optimal.
Hence what is needed is a method and an apparatus for performing convergecast operations in a wireless sensor network without the above-described problems.